Pharmaceutical Suspensions: Size and Stability

Pharmaceutical Suspensions: Particle Size and Stability

• Particle Size Range: Most pharmaceutical suspensions contain particles between 1 and 50 µm.

• Micro Pulverization: A rapid and inexpensive method to produce fine drug powders (10-50 µm) using high-speed mills. Suitable for oral and topical suspensions.

• Fluid Energy Grinding/Jet Milling/ Micronizing: Used to create particles smaller than 10 µm. High-velocity compressed air shears particles in a confined space, creating micronized particles. Suitable for parenteral or ophthalmic suspensions.

• Spray Drying: Produces extremely small particles. A solution is sprayed into a cone-shaped apparatus where heated, dry air rapidly dries the solution. Mortar and pestle methods can't achieve this level of particle size control.

• Particle Size and Settling: Reducing particle size slows settling but extremely fine particles can form a compact cake. Avoiding excessive fineness is important.

• Particle Shape and Stability: Particle shape affects caking and stability. For example, symmetrical barrel-shaped particles are more stable than needle-shaped ones.

• Flocculation: Intentional formation of a loose aggregation (floc) of particles, held together by weak bonds, prevents rigid cohesion.

• Suspension Thickening Agents: Substances like carboxymethylcellulose, methylcellulose, microcrystalline cellulose, polyvinyl pyrrolidone, xanthan gum, and bentonite thicken the dispersion medium to aid in suspending the particles.